Screen device for pneumatic transport equipment

ABSTRACT

A screen device for fine-grain materials for use in pneumatic transport equipment. The device comprises screen means inside a transfer pipe and means in the portion of said transfer pipe upstream of said screen means for blowing additional air into said transport pipe.

United States Patent 11 1 Hagelstam 1 Nov. 11, 1975 [5 SCREEN DEVICE FOR PNEUMATIC 550911 12/1895 Fell 209/250 x EQUIPMENT 1 i892: 7121; fizz/328::

Q {1T5 1 1 .1 -2 Inventor: 1 Hjalmar Hagelstam, Helsinki 1.272.682 7/1918 Lenders 1 209/134 x Finland 1530,19 3/1925 Montgomen 09/250 X 1.573.373 2/1926 (22.. 11 1 209/250 X [73] Asslgnee: 3' Karl HelsmkL 2874.840 2/1959 51111212011 09/262 x Fmland 2.910731 11/1959 Moore 1. 209/250 x 2 Filed: Sept. 11 1973 3354.766 6/1966 Anderson 209/250 X 3685.651 8/1972 Gruher 209/133 1211 Appl. No.: 396,159

Primary E.\'u/ni/le/'-Robert Halper 130] Foreign Application Priority Dat AHOY/18)., Agent, or Fir/71Ladas, Parry, Von Gehr.

Sept. 12, 1972 hnland 2508/7 Goldsmlth Deschamps [52] US. Cl. 209/3; 209/250; 302/29 [57] ABSTRACT 23 'g B03!) 7/706 A screen device for fine-grain materials for use in 1 easrc '1 pneumatic transport equipment. The device comprises H 13 2 3- screen means inside a transfer pipe and means in the 58 portion of said transfer pipe upstream of said screen means for blowing additional air into said transport [56] References Cited pipe.

UNITED STATES PATENTS 90.097 5/1869 Hanford 209/250 x 6 2 Drawmg F'gures i n n US. Patent Nov. 11, 1975 3,918,585

SCREEN DEVICE FOR PNEUMATIC TRANSPORT EQUIPMENT The subject of the present invention is a screen device for fine-grain materials, such as flour, to be used in pneumatic transport equipment, which screen device consists of a screen arranged inside the transport pipe.

When fine-grain materials, such as flour, are transferred pneumatically, for example, from the truck tank into the warehouse, a need frequently arises to screen the material by separating particles larger than the screen mesh from the material to be transferred. In the case of flour the practice has so far been that the flour has been moved by means of compressed air along a transfer pipe into an intermediate tank, in which the transfer air has been separated from the material, for example, by means of a cyclone. From the intermediate tank the material has been conducted by means of gravitation to the screen and from the screen through a feeding lock into another compressed-air operated transfer pipe, which has carried the material to the destination. The use of an intermediate tank and of a feeding lock has been due to the fact that it has not been possible to connect the screen directly to the transfer pipe under pressure, because therein the screen would be rapidly blocked.

The known equipment described above is complicated and expensive, because it usually comprises two compressors, an intermediate tank with possible cyclone, and a feeding lock. Since the flour passes through the screen only by means of the force of gravitation, the screen area must be made very large in order to reach a satisfactory degree of passing through.

For a long time it has already been known that when mixed with air, the flour is in a way fluidized and then, in the same way as liquids passes through very narrow passages, and the present invention is based on the idea, according to which the blocking of the screen is prevented by making use of this phenomenon. This has been achieved in the screen device in accordance with the invention mainly so that the portion of the transfer pipe upstream of the screen has equipment for blowing additional air into the interior of the said portion.

As was already mentioned above, an ordinary screen is already blocked after an operation of a couple of minutes if it is placed directly in the pressure-air pipe, because the phenomenon of fluidization cannot affect sufficiently strongly. By increasing the quantity of air in the way in accordance with the invention, a strong fluidization of the flour is produced, as a result of which the screen is not blocked and can be positioned directly in the pneumatic transport pipe, because the pressure therein does not disturb the operation of the screen. This involves considerable advantages, for the intermediate tank and the feeding lock can be omitted as unnecessary and the size of the screen can be reduced considerably as compared with known screens of the corresponding capacity, because the overpressure in the transfer tube forces the particles to pass through the screen with a high speed.

The invention will be described below more closely with reference to the attached drawing, wherein FIG. 1 shows a schematic view of a pneumatic transport equipment and FIG. 2 shows a side view of the screen device in partial section.

FIG. 1 shows compressor 1 and the outgoing pneumatic transfer pipe 2, which is connected with a feeding lock 3 and a screen device 4.. Before the feeding lock a by-passing pipe 5 is branched from the transfer pipe to the screen device 4.

According to FIG. 2, the screen device 4 consists of two funnels 6 and 7, placed one opposite the other, between which there is a screen 8. The funnel 6 of the inlet direction has an annular air space 9, from which holes 10 in the funnel wall provide passage into the funnel. The air space 9 is connected with the by-passing pipe 5 through a cock 11.

The transport equipment operates as follows:

The compressor 1 feeds air, for example at an overpressure of 1 kg per square cm, into the transfer pipe 2, into which the material to be transferred is at the same time also being fed from the feeding lock 3. The material passes into the screen device 4, in which air as added into same by means of the by-passing pipe 5, the air space 9 and the holes 10. As a result of this the material is fluidized and sufficiently small particles easily pass through the screen 8 without blocking it.

Particles larger than the mesh of the screen remain in the funnel 6 and can be removed by providing the pipe 2 with two screen devices 2, arranged in parallel (not shown) and which are alternatingly connected to the pipe. When one screen device is connected to the pipe, the other one is at the emptying pipe for removal of the large particles from the screen device. In such a case the transfer of flour need not be interrupted during cleaning of the screen devices.

Alternatively, the larger particles collected in the screen can be removed through a removal pipe provided with a blocking plate. This can take place always when material is not being transferred in the pneumatic transport equipment, thus, for example, after the transfer of the contents of each container of a truck if transfer of flour from a transport truck into a tank is concerned.

It is to be noticed that the attached drawings and the relating description are only intended to illustrate certain preferable embodiments of the invention. Thus, additional air can be introduced in the funnel 6 in many ways, for example through a nozzle introduced in the funnel or through a porous wall that allows air to pass through and that is positioned at the holes 10. The emptying can, moreover, be made automatic by combining the operation of the feeding lock 3 with the operation of the locking plate of the removal pipe as con trolled by a clock or by a tachometer. Neither is it necessary that the funnels 6 and 7 have the shape of a funnel, but they can be, for example, straight pipes whose diameter is constant.

What I claim is:

l. A screen device for fine-grain materials, especially flour, to be used in pneumatic transport equipment comprising:

a source of pneumatic pressure;

a transfer pipe connected to said source of pneumatic pressure; means connected to said transfer pipe for feeding said material into said transfer pipe in order to transport said material along the pipe entrained in a flow of air from said source;

a screen connected to said transfer pipe downstream of said feeding means, and arranged transversely to the transfer pipe; and

stationary means connected to a source of compressed air and defining an array of small apertures, which array extends completely around the interior ofa portion of the transfer pipe located immediately upstream of the screen to form a multiplicity of small, closely spaced air streams in order to mix effectively substantially all of said fine-grain material moving towards said screen with the air of said streams thereby to fluidize the fine-grain material, the pressure of the air of the streams being substantially the same as the transport pressure of said flow of air.

2. A screen device in accordance with claim 1, wherein the stationary means include means defining an annular air space which surrounds said portion of the transfer pipe and is connected to said source of compressed air.

3. A screen device in accordance with claim 1,

wherein said apertures are formed in a wall of said portion and communicate with said annular air space.

4. A screen device in accordance with claim 1, wherein said apertures are defined by a porous wall of said portion.

5. A screen device in accordance with claim 1, wherein the cross-section of the interior of said portion of the transfer pipe increases towards the screen both upstream and downstream of the screen.

6. A screen device in accordance with claim 1, wherein said source of compressed air and said source of pneumatic pressure are one and the same, the transfer pipe being provided with a branch pipe departing from said transfer pipe at a location between said source of pneumatic pressure and said feeding means and being connected to said stationary means. 

1. A screen device for fine-grain materials, especially flour, to be used in pneumatic transport equipment comprising: a source of pneumatic pressure; a transfer pipe connected to said source of pneumatic pressure; means connected to said transfer pipe for feeding said material into said transfer pipe in order to transport said material along the pipe entrained in a flow of air from said source; a screen connected to said transfer pipe downstream of said feeding means, and arranged transversely to the transfer pipe; and stationary means connected to a source of compressed air and defining an array of small apertures, which array extends completely around the interior of a portion of the transfer pipe located immediately upstream of the screen to form a multiplicity of sMall, closely spaced air streams in order to mix effectively substantially all of said fine-grain material moving towards said screen with the air of said streams thereby to fluidize the fine-grain material, the pressure of the air of the streams being substantially the same as the transport pressure of said flow of air.
 2. A screen device in accordance with claim 1, wherein the stationary means include means defining an annular air space which surrounds said portion of the transfer pipe and is connected to said source of compressed air.
 3. A screen device in accordance with claim 1, wherein said apertures are formed in a wall of said portion and communicate with said annular air space.
 4. A screen device in accordance with claim 1, wherein said apertures are defined by a porous wall of said portion.
 5. A screen device in accordance with claim 1, wherein the cross-section of the interior of said portion of the transfer pipe increases towards the screen both upstream and downstream of the screen.
 6. A screen device in accordance with claim 1, wherein said source of compressed air and said source of pneumatic pressure are one and the same, the transfer pipe being provided with a branch pipe departing from said transfer pipe at a location between said source of pneumatic pressure and said feeding means and being connected to said stationary means. 